Optional Live production tracing

[Jorropo]

Currently when enabling open-telemetry tracing performance and resource usage seriously suffers, this is good enough for debugging scenarios but can't be ran continuously to production.

We want to be able to debug ipfs.io production with tracing when things goes wrong.

We needs theses two features:

• Be able to disable automatic tracing everytime we create a span even tho tracing is configured on the map.
  But it needs to passthrough if we are already tracing.
• Add some flag on the gateway (and maybe also RPC) to optin-in in tracing.